Among the myriad devices employing ear tips, stethoscopes and audio headsets are among the most common. Some stethoscopes may employ a spring-loaded means for forcing the ear tips into the user's ears in an attempt to create a sound-proof seal that maximizes the wearer's ability to hear only the desired sound free of ambient interference. This general design creates two related problems for the user. First, the exterior ear canal is rather sensitive to pressure and second, the ear canal varies in size and shape from person to person. Thus, hard conventional ear tips can cause serious discomfort by applying high pressure to the irregular surface of the user's ear canal. Furthermore, such hard ear tips form a poor acoustic seal with the ear, allowing ambient sound to infiltrate the ear canal and obscure the sound delivered by the device.
These problems of comfort and sound exclusion have been addressed in a number of ways, both as to ear tips and as to ear plugs. For example, soft, malleable materials such as air encased in a plastic bladder (U.S. Pat. Nos. 3,895,627, 3,768,470, and 4,089,332), a mushroom shaped soft rubber head (U.S. Pat. No. 3,618,600), malleable plastic (U.S. Pat. No. 4,552,137), and closed-cell foam encased in a plastic shell (U.S. Pat. No. 4,434,794) are described in the patent literature.
Design variations such as a flared, horn-shaped ear tip designed to fit over, rather than into, the ear canal (U.S. Pat. No. 3,303,902), various shapes with skirt-like flanges that insert into the ear canal (U.S. Pat. Nos. 4,564,009 and 3,896,801, G.B. patent No. 2,173,110 A), and soft mushroom-shaped ear tips (U.S. Pat. Nos. 4,055,233 and 3,539,031) have appeared as well. All such inventions rely upon pressure to create a good acoustic seal.
A further design, appearing in U.S. Pat. No. 4,552,137, teaches a solution where a tight fit is attained not by pressure but by a layer of adhesive on the ear tip's surface.